Magnetic components provided with a coil having a winding portion formed by winding a wire and a magnetic core on which the coil is disposed are provided in various types of products such as automobiles, electrical equipment, and industrial machinery. Magnetic materials used for magnetic cores include a powder compact disclosed in, for example, JP 2009-070885A, and composite materials containing a soft magnetic powder and a resin that are disclosed in, for example, JP 2009-176974A and JP 2011-181747A.
JP 2009-070885A discloses a reactor as a magnetic component, and discloses a magnetic core including a powder compact and a plate-shaped gap material (spacer) made of a non-magnetic material such as alumina. This powder compact is manufactured by compression molding a metal magnetic powder coated with an insulating coating and then performing heat treatment on the compression-molded product to remove strain that has been introduced into the metal particles during compression molding. In JP 2009-070885A, it is stated that hysteresis loss of the powder compact can be reduced through the above-described heat treatment.
It is desired to develop a composite material having excellent direct current superposition characteristics, low iron loss (sum of hysteresis loss and eddy loss), and also excellent strength as a magnetic material for magnetic components or the like.
Here, a magnetic core of a magnetic component is desired to satisfy the following requirements: (A) it has excellent direct current superposition characteristics, or, in other words, changes in relative permeability are small from a low magnetic field up to a high magnetic field; (B) it has large saturation magnetization, or, in other words, it is unlikely to be magnetically saturated; and (C) it has excellent high-frequency characteristics, or, in other words, it has low iron loss in a high frequency range.
In a composite material containing a soft magnetic powder and a resin, the resin, which is a constituent ingredient, is generally a non-magnetic material, and the resin can therefore be regarded as a magnetic gap. Accordingly, if a magnetic core of a magnetic component is composed of the above-described composite material, unlike the case in which the magnetic core is composed of the above-described powder compact, the gap material can be omitted, and thus the magnetic core has the advantage of (A) having excellent direct current superposition characteristics. Moreover, with the above-described composite material, if the soft magnetic powder content is increased, (B) saturation magnetization can be increased.
However, when the filling ratio of the soft magnetic powder is increased, nonuniform dispersion of the soft magnetic powder may occur, and contact between powder particles may occur if the soft magnetic powder is a metal powder. These problems may result in a decrease in direct current superposition characteristics, an increase in eddy-current loss, a decrease in strength due to concentrated distribution of the soft magnetic powder, and the like.
Furthermore, as shown in a test example, which will be described later, it was found that, in the composite material, stress and the like that may be applied to the soft magnetic powder and the resin during the manufacturing process may cause an increase in iron loss and a decrease in strength. In this respect, in the case of the above-described powder compact, the hysteresis loss can be effectively reduced if heat treatment is performed at a particularly high temperature after performing compression molding. However, in the case of the composite material, heat treatment at a high temperature is difficult because the composite material contains resin. For this reason, it is desirable to obtain a composite material having excellent direct current superposition characteristics, low iron loss, and high strength without performing heat treatment.
In view of the above-described circumstances, the present invention provides a composite material having excellent direct current superposition characteristics, low iron loss, and high strength.
Moreover, the present invention provides a magnetic core for a magnetic component, the magnetic core having excellent direct current superposition characteristics, low loss, and high strength; a reactor including the magnetic core having excellent direct current superposition characteristics, low loss, and high strength; and a converter and a power conversion device that include the reactor.